Pumps

The failure of a sealant where a moving shaft meets a stationary casting is a source of fugitive gas emissions. Figure

Pump stuffing box

Fluid end

Pump stuffing box

Fluid end

Stationary element

Possible leak area

Rotating seal ring

FIG. 5.24.4 Typical design of a packed, sealed pump shaft. (Reprinted from U.S. EPA, 1984.)

Gland ring

Stationary element

Possible leak area

Seal liquid Seal liquid out (top) in (bottom)

Rotating seal ring

FIG. 5.24.4 Typical design of a packed, sealed pump shaft. (Reprinted from U.S. EPA, 1984.)

5.24.4 shows the possible leak area. Lubricants between the rotating shaft and the stationary packing control the heat generated by friction between the two materials.

The following techniques can hold fugitive emissions to a minimum:

Equipping pumps with double, mechanical seals that have liquid buffer zones and alarms or automatic pump shut-offs for seal failures (see Figure 5.24.5). The effective use of mechanical seals requires closed tolerances. Shaft vibration and misalignment induce radial forces and movement, which can damage both seals and bearings. The primary causes of radial shaft motion include poor alignment of the shaft with the motor connected to the pump, poor baseplate installation, incorrect operating conditions, and loose or failed bearings (Clark and Littlefield 1994). Continuously coating bearings with lubricants keeps the surfaces free of debris. Using canned-motor pumps (see Figure 5.24.6). These units are closed-couple designs in which the cavity housing the motor rotor and the pump casing are interconnected. As a result, the pump bearings run in the process liquid, and all seals are eliminated. Adopting diaphragm and magnetic-drive pumps. These two pumps do not require a sealant to control leakage.

Adams (1992) discusses the selection and operation of mechanical seals.

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